Ziang Liu

Earth Abundant Fe/Mn-Based Layered Oxide Interconnected Nanowires for Advanced K-Ion Full Batteries

K-ion battery (KIB) is a new-type energy storage device that possesses potential advantages of low-cost and abundant resource of K precursor materials. However, the main challenge lies on the lack of stable materials to accommodate the intercalation of large-size K-ions. Here we designed and constructed a novel earth abundant Fe/Mn-based layered oxide interconnected nanowires as a cathode in KIBs for the first time, which exhibits both high capacity and good cycling stability. On the basis of advanced in situ X-ray diffraction analysis and electrochemical characterization, we confirm that interconnected K0.7Fe0.5Mn0.5O2 nanowires can provide stable framework structure, fast K-ion diffusion channels, and three-dimensional electron transport network during the depotassiation/potassiation processes. As a result, a considerable initial discharge capacity of 178 mAh g-1 is achieved when measured for KIBs. Besides, K-ion full batteries based on interconnected K0.7Fe0.5Mn0.5O2 nanowires/soft carbon are assembled, manifesting over 250 cycles with a capacity retention of ∼76%. This work may open up the investigation of high-performance K-ion intercalated earth abundant layered cathodes and will push the development of energy storage systems.

Interface-modulated approach toward multilevel metal oxide nanotubes for lithium-ion batteries and oxygen reduction reaction

Metal oxide hollow structures with multilevel interiors are of great interest for potential applications such as catalysis, chemical sensing, drug delivery, and energy storage. However, the controlled synthesis of multilevel nanotubes remains a great challenge. Here we develop a facile interface-modulated approach toward the synthesis of complex metal oxide multilevel nanotubes with tunable interior structures through electrospinning followed by controlled heat treatment. This versatile strategy can be effectively applied to fabricate wire-in-tube and tube-in-tube nanotubes of various metal oxides. These multilevel nanotubes possess a large specific surface area, fast mass transport, good strain accommodation, and high packing density, which are advantageous for lithium-ion batteries (LIBs) and the oxygen reduction reaction (ORR). Specifically, shrinkable CoMn2O4 tube-in-tube nanotubes as a lithium-ion battery anode deliver a high discharge capacity of ~565 mAh·g−1 at a high rate of 2 A·g−1, maintaining 89% of the latter after 500 cycles. Further, as an oxygen reduction reaction catalyst, these nanotubes also exhibit excellent stability with about 92% current retention after 30,000 s, which is higher than that of commercial Pt/C (81%). Therefore, this feasible method may push the rapid development of one-dimensional (1D) nanomaterials. These multifunctional nanotubes have great potential in many frontier fields.

A synergistic effect between layer surface configurations and K ions of potassium vanadate nanowires for enhanced energy storage performance

Layered metal vanadates, especially alkali metal vanadates, have been extensively studied in energy storage. Generally, vanadates exhibit more stable electrochemical performance than pristine vanadium oxides, and different vanadates also vary in the performance. However, the detailed mechanisms of the variation in the performance of vanadates and vanadium oxides are poorly explored. Here we choose and construct three typical layered vanadium-based nanowires (V2O5, KV3O8 and K0.25V2O5), and investigate the origin of the enhanced electrochemical performance of the potassium vanadates compared to V2O5, based on crystal structure analysis, electrochemical tests, ex situ ICP measurements and in situ XRD detections. We demonstrate a synergistic effect between layer surface configurations and K ions of potassium vanadate nanowires, which leads to the great improvement in electrochemical stability of K0.25V2O5. The layer surface configuration of K0.25V2O5 only consists of single-connected oxygen atoms, which provides strong interaction with the K ions. And the stabilized K ions act as “pillars” between interlayers to protect the layered structures from collapse in the charge/discharge process. This work provides a further insight into alkali metal vanadates, and benefits the design of ideal electrode materials in the energy storage field.

General Oriented Synthesis of Precise Carbon-Confined Nanostructures by Low-Pressure Vapor Superassembly and Controlled Pyrolysis

Earth-abundant metal-based nanostructured materials have been widely studied for potential energy conversion and storage. However, controlled synthesis of functional nanostructures with high electron conductivity, high reaction activity, and structural stability is still a formidable challenge for further practical applications. Herein, for the first time, we develop a facile, efficient, and general method for the oriented synthesis of precise carbon-confined nanostructures by low-pressure vapor superassembly of a thin metal-organic framework (MOF) shell and subsequent controlled pyrolysis. The selected nanostructured metal oxide precursors not only act as metal ion sources but also orient the superassembly of gaseous organic ligands through the coordination reactions under the low-pressure condition, resulting in the formation of a tunable MOF shell on their surfaces. This strategy is further successfully extended to obtain various precise carbon-confined nanostructures with diverse compositions and delicate morphologies. Notably, these as-prepared carbon-confined architectures exhibit outstanding electrochemical performances in water splitting and lithium storage. The remarkable performances are mainly attributed to the synergistic effect from appropriate chemical compositions and stable carbon-confined structures. This synthetic approach and proposed mechanism open new avenues for the development of functional nanostructured materials in many frontier fields.

General oriented assembly of uniform carbon-confined metal oxide nanodots on graphene for stable and ultrafast lithium storage

A facile and general method for the oriented assembly of uniform carbon-confined metal oxide nanodots on graphene was developed via a well-designed process including surfactant-induced assembly, mismatched coordination reaction and subsequent in situ carbonization. On the basis of experimental analyses and density functional theory calculations, the key mismatched coordination reaction mechanism is clearly revealed, resulting in the formation of small amorphous metal–ligand complexes. This versatile oriented assembly strategy is then generally applied to obtain various carbon-confined metal oxide (SnO2, Cr2O3, Fe3O4 and Al2O3) nanodots on graphene. Notably, the as-prepared C@SnO2@Gr electrode as an LIB anode material possesses a high reversible discharge capacity of 702 mA h g−1 and an excellent capacity retention of over 100% tested at 2 A g−1 after 1200 cycles.

Facile template-free synthesis of uniform carbon-confined V2O3 hollow spheres for stable and fast lithium storage

A facile template-free method has been successfully developed to synthesize uniform nitrogen-doped carbon-confined V2O3 hollow spheres by a mismatched coordination reaction, an inside-out Ostwald-ripening solvothermal process and subsequent heat treatment. Notably, the delicate composite as an anode material displayed superior rate capability and excellent cycling stability for lithium-ion batteries.

Ni foam supported NiO nanosheets as high-performance free-standing electrodes for hybrid supercapacitors and Ni–Zn batteries

Herein, Ni foam (NF) supported NiO nanosheets with a NF@NiO core@shell structure have been synthesized by a facile etching-reoxidation method. The obtained NF@NiO can function as high-performance free-standing electrodes for both hybrid supercapacitors and Ni–Zn batteries. When employed as the cathode for hybrid supercapacitors, the NF@NiO exhibits a high areal capacitance of 2.01 F cm−2 at 8 mA cm−2. By coupling with an FeOOH anode, the assembled NF@NiO//FeOOH asymmetric supercapacitor delivers a peak energy density of 2.15 mW h cm−3 and a peak power density of 2.75 W cm−3. A rechargeable Ni–Zn battery is also assembled using NF@NiO as the cathode. The NF@NiO//Zn battery demonstrates a high maximum energy density (25.6 μW h cm−2) and an impressive power density (86.48 mW cm−2) with remarkable cycling durability (84.7% capacity retention for 10 000 cycles). These features make the free-standing NF@NiO a promising candidate for electrochemical energy storage.

General and precise carbon confinement of functional nanostructures derived from assembled metal–phenolic networks for enhanced lithium storage

Carbon coating strategies have been widely used to enhance the electrochemical performance of electrode materials. However, several issues, including substrate material selectivity, hard control on precise coatings and a limited enhancement of electronic conductivity, hinder the conventional strategies from further practical application. Here, we develop a general, facile and programmable strategy to precisely construct carbon-confined functional nanostructures with high conductivity via metal–phenolic network (MPN) assembly and subsequent controlled pyrolysis. The instantaneous MPN assembly is realized via the coordination reaction between metal ions and phenolic ligands, and the thickness of the MPN shell can be well controlled by simply repeating the rapid assembly procedure. This strategy is further successfully extended to versatile electrode materials with diverse nanostructures and rich compositions. As a proof of concept, the as-synthesized carbon-confined SnO2 hollow spheres with Fe2O3 nanodots embedded in a carbon shell (SnO2@C–Fe2O3) exhibit a high reversible discharge capacity of 1203 mA h g−1 after 100 cycles at 0.2 A g−1, an excellent cycling stability with a capacity retention of 86% after 1000 cycles at 1 A g−1, and a high capacity of 830 mA h g−1 at a higher rate of 5 A g−1. These remarkable performances are attributed to the unique carbon shell, which provides the robust structure to buffer the drastic volume variation and the enhanced electronic conductivity. This programmable and controllable carbon coating strategy opens a new avenue for the design of carbon-incorporated electrode materials for high-performance energy storage.

Recent advances in nanowire-based flexible freestanding electrodes for energy storage

The rational design of flexible electrodes is essential for achieving high performance in flexible and wearable energy-storage devices, which are highly desired with fast-growing demands for flexible electronics. Owing to the one-dimensional structure, nanowires with continuous electron conduction, ion diffusion channels, and good mechanical properties are particularly favorable for obtaining flexible freestanding electrodes that can realize high energy/power density, while retaining long-term cycling stability under various mechanical deformations. This Minireview focuses on recent advances in the design, fabrication, and application of nanowire-based flexible freestanding electrodes with diverse compositions, while highlighting the rational design of nanowire-based materials for high-performance flexible electrodes. Existing challenges and future opportunities towards a deeper fundamental understanding and practical applications are also presented.